A lot of times the same room can have different flooring or an invisible separation. Eg: Open living rooms with kitchens, dining areas etc.
A room/space can be separated from another room without a wall. To do this, before drawing a room, select "None" for wall, and draw the room.
The same result can be achieved after drawing the room by making one or more walls "hidden". To do this, select the wall, and use the "hide" menu on the popup.